San Francisco Solar Maps
A Google Maps mashup of San Francisco Solar Activity was launched by the San Francisco Department of the Environment and CH2M HILL in June, 2007. It is located at sf.solarmap.org. There are several problems with this map. I will comment on two important errors.
The sf.solarmap uses the same figure for solar electric output (5 kWh per day per kilowatt system) for every location in the City as of July, 2008, more than one year after the sf.solarmap was launched. To see this, enter the SFDOE downtown address of 11 Grove St., and you get the result:*
Try a house in the outer Sunset, 2494 44th Ave., and the result is:*
In each of the above examples, dividing the figures in line 2 by the corresponding figures in line 1 gives 1825 kWh/yr or 5 kWh per day per kilowatt system.
Everyone knows, however, that the west side of the City is foggier than the east side and gets less sunshine. This has been quantified for several years by the 11 SFPUC solar monitoring stations, whose findings as of the beginning of 2008 are summarized in the San Francisco Solar Map. The west side of the City averaged 4.1 to 4.2 kWh/day/m2 insolation and the east side 4.5 to 4.6 kWh/day/m2. The citywide average was less than 4.5 kWh/day/m2.
But there is a larger error. The sf.solarmap uses 5 kWh per day per kilowatt system as output. Actually, the output, kWh per day per kilowatt system, is only about 2/3 of the input (insolation) kWh/day/m2 according to California Energy Commission 2001 guidelines. This is demonstrated by the Moscone Center Solar Power System and other locations.
So a more accurate figure for output is about 3 kWh per day per kilowatt system. The figures on the sf.solarmap are too high.
Robert Karis
* 2/10/09 The estimated solar PV potential and electricity produced in the sf.solarmap have inexplicably been increased by a factor of 2-4 times. However, the output is still incorrect, 1825 kWh/yr or 5 kWh per day per kilowatt system in different areas of the City. View comments for update.
The sf.solarmap uses the same figure for solar electric output (5 kWh per day per kilowatt system) for every location in the City as of July, 2008, more than one year after the sf.solarmap was launched. To see this, enter the SFDOE downtown address of 11 Grove St., and you get the result:*
| Estimated solar PV potential: | 7 - 15 kW |
| Estimated electricity produced: | 12775 - 27375 KWh/yr |
| Estimated solar PV potential: | 2 - 3 kW |
| Estimated electricity produced: | 3650 - 5475 KWh/yr |
Everyone knows, however, that the west side of the City is foggier than the east side and gets less sunshine. This has been quantified for several years by the 11 SFPUC solar monitoring stations, whose findings as of the beginning of 2008 are summarized in the San Francisco Solar Map. The west side of the City averaged 4.1 to 4.2 kWh/day/m2 insolation and the east side 4.5 to 4.6 kWh/day/m2. The citywide average was less than 4.5 kWh/day/m2.
But there is a larger error. The sf.solarmap uses 5 kWh per day per kilowatt system as output. Actually, the output, kWh per day per kilowatt system, is only about 2/3 of the input (insolation) kWh/day/m2 according to California Energy Commission 2001 guidelines. This is demonstrated by the Moscone Center Solar Power System and other locations.
So a more accurate figure for output is about 3 kWh per day per kilowatt system. The figures on the sf.solarmap are too high.
Robert Karis
* 2/10/09 The estimated solar PV potential and electricity produced in the sf.solarmap have inexplicably been increased by a factor of 2-4 times. However, the output is still incorrect, 1825 kWh/yr or 5 kWh per day per kilowatt system in different areas of the City. View comments for update.
Here are the current figures for the above addresses in the SF solar map:
11 Grove Street downtown (district 6, insolation 4.6 kWh/m2/day):
Estimated solar PV potential: 17 - 34 kW
Estimated electricity produced: 31025 - 62050 KWh/yr
Electricity produced (31,025 kWh/yr)/(17 kW) = 1,825 kWh per kW system per year, or 5 kWh per kW system per day.
2494 44th Ave. in the Sunset (district 4, insolation 4.1 kWh/m2/day):
Estimated solar PV potential: 7 - 13 kW
Estimated electricity produced: 12775 - 23725 KWh/yr
Electricity produced (12,775 kWh/yr)/(7 kW) = 1,825 kWh per kW system per year, or 5 kWh per kW system per day.
The results for output (5 kWh per kW system per day) continue to be the same in different parts of the city, despite the fact that the solar inputs are different.
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After several emails from me over a year's time, the sf.solarmap finally gives different results for the different districts, 4.6 and 4.1 kWh per kW system per day for the examples in the previous posts.
It's still true, as I stated in my first post on this topic, that the actual output, kWh/kW system, is less than the input, kWh/m2. Also, the "Estimated solar PV potential" for each house on the sf.solarmap was increased earlier this year. In the case of my house, the new estimate is at least twice what is possible. So the results in the sf.solarmap are still too high.
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Response to a question: you may use the data on the website, provided you give proper credit. Links to commercial websites are not accepted.
Thanks.
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